What can kill you,
But can save you too?
What can be blue,
But can be clear too?
What is safest to drink
When it gets hot?
Live without this
You shall not.

Answer

Water

What can kill you: Water can kill you by floods, whirlpool, etc.
But can save you too: It can save you when you're dehydrated.
What can be blue: The water in the oceans are blue due to reflection.
But can be clear too: The water that you drink always looks clear.
What is safest to drink
When it gets hot: Sometimes you have to boil water before you drink it to kill off any bacteria in it.
Live without this
You shall not: You can't live without water.Hide